The subject matter of this invention relates generally to ground fault indicators and specifically to low energy magnetic ground fault indicators.
Ground fault indicators of various types have been provided in the past for signalling an observer that a circuit breaker has tripped due to the influence of a ground fault. Devices which may be utilized with circuit breakers for this purpose are taught in a descriptive bulletin distributed under the registered trademark MINELCO. Various indicators are taught therein under the bulletin titles B-11A through B-13A, M-11A, M-12, M-13, M-14, M-16, M-17 and C-11. Furthermore, light reflecting status indicators are taught in a descriptive bulletin of Ferranti-Packard Ltd., Electronics Division, Toronto, Ontario, Canada. The descriptive bulletin is numbered 372 revised 0174. According to the latter-mentioned descriptive bulletin, patents covering the light reflecting status indicator are as follows: Canadian Pat. No. 641,350 and No. 771,356; U.S. Pat. No. 3,140,553 and United Kingdom Pat. No. 934,001. The latter descriptive bulletin also indicates that other patents are pending. The devices taught in both the latter and the former descriptive bulletins generally comprise a pivotally mounted permanent magnet which is disposed in the air gap of an electromagnet. The electromagnet may be energized temporarily to provide magnetic poles which are in opposition to the poles of the permanent magnet. This may cause the disposition of the permanent magnet to change from a first stable state to a second stable state, thus providing a mechanical indication of the occurrence of an event. It would be advantageous if an indicating device which utilizes electromagnetic principles and mechanical principles could be provided where the indicating means itself is not a permanent magnet, where a relatively low energy pulse could be provided to an electromagnetic means to cause a change in status indication and where the change in status indication is dramatic and obvious. Prior art devices teach members which are colored differently on either side thereof. Consequently, as the change in magnetic field causes movement of the magnetic member, one color is replaced by the other, thus providing the status indication previously described. Other U.S. patents which teach the utilization of electromagnetics or permanent magnets and/or mechanical moving devices are as follows: U.S. Pat. No. 3,221,246, issued Nov. 30, 1965 to C. B. Sanborn, Jr. This device teaches the utilization of two electromagnetic cores with a common reluctance changing device to provide an output electrical signal which is related to the disposition of the reluctance device. U.S. Pat. No. 2,540,845, issued Feb. 6, 1951 to C. A. Thomas teaches an electromagnetic keeper which is spring-biased to provide an alternate path for magnetic flux when an armature device is moved in a certain direction. U.S. Pat. No. 3,825,915, issued July 23, 1974 to R. C. Dow teaches a device for indicating the presence of an electric grounding means. The absence of the ground means is indicated electrically. U.S. Pat. No. 3,823,369, issued July 9, 1974 to R. R. P. Sinha teaches an electromechanical device which causes the illumination of a lamp for determining the condition of a transformer. U.S. Pat. No. 3,213,396, issued Oct. 19, 1965 to M. Berger teaches the indication of the disposition of a mechanical element by utilizing a three-leg transformer device having an air gap in the middle leg thereof. U.S. Pat. No. 3,128,441, issued Apr. 7, 1964 to E. W. Johnson et al. teaches a variable dynamo transformer having a linearly movable armature where the relative placement of the armature is responsible for the magnitude of an electrical signal at the output of the device. Finally, U.S. Pat. No. 3,101,462, issued Aug. 20, 1963 to E. L. Swainson teaches a linear motion signal producing magnetic transducer for producing a signal for indicating the linear position of an element. None of the above-mentioned descriptive bulletins or patents teach a flux shifting device for providing a low energy resettable mechanically forced but electromagnetically actuated indication of status. Furthermore, none of the above-mentioned inventions show status indication in relationship to the ground fault activity of a circuit breaker.
U.S. patents which are assigned to the assignee of the present invention which teach circuit breaker apparatus and sensing and control circuitry which may be utilized in conjunction with the present status indicating circuit are as follows: U.S. Pat. No. 3,543,094, issued Nov. 24, 1970 to W. H. South et al.; U.S. Pat. No. 3,602,783, issued Aug. 31, 1971 to J. C. Engle et al.; U.S. Pat. No. 3,634,730, issued Jan. 11, 1972 to J. T. Wilson; U.S. Pat. No. 3,660,722, issued May 2, 1972 to J. T. Wilson et al.; U.S. Pat. No. 3,666,994, issued June 18, 1970 to J. D. Watson et al. and U.S. Pat. No. 3,689,801, issued Sept. 5, 1972 to J. C. Engle et al.
U.S. Patents which are issued to the assignee which teach circuit breaker apparatus utilizing a flux shifting apparatus for tripping include for example, U.S. Pat. No. 3,783,423, issued Jan. 1, 1974 to A. E. Mater and J. A. Wafer.